We have read with interest the paper by Krishnakumar et al.¹ We have studied 18 children with retinoblastoma using immunohistochemical detection of P-glycoprotein by the mouse monoclonal antibody HYB-241 in frozen section tumour samples. Like Krishnakumar et al, we found limited expression of P-glycoprotein in retinoblastoma cells since only four of the 18 samples were positive. However, six of 18 samples had P-glycoprotein positivity in tumour associated endothelial cells. Contrary to Krishnakumar et al, we had …